Ion-exchangeable media are frequently employed in chromatography, ion exchange, and catalyst applications. Ion-exchangeable media are solid phase or gel-type materials that contain ion-exchange sites that carry ion-exchangeable cations or anions. The form of the ion-exchangeable media, which refers to the type and quantity of ion-exchangeable cations or anions carried by the media, provides certain unique properties to the media that impart unique functionality to the media. For example, ion-exchange resins in calcium form have unique properties for chromatographic separation of sugars, zeolites containing transition metals have been used as catalysts, and ion-exchange resins in silver form have been used to separate certain hydrocarbons. Although there is a broad spectrum of ion-exchangeable media with many unique properties, only a limited number of ion-exchangeable media forms are available commercially, such as sodium, calcium, potassium, and hydrogen form cation-exchange media and chloride and hydroxide form anion-exchange media. Ion-exchangeable media containing a specific concentration of species, such as 5% calcium or 10% silver are not readily available and, as such, the process of the invention provides a means to convert commercially available forms of ion-exchangeable media to a specific form for a specific application.
The goal of the preparation is to change the media from a standard, commercially available form to a specialty form with a particular usefulness as a processing media. The usefulness of the media is determined by its applicability to separate, purify, or react compounds within the context of an adsorption or catalytic type process. Various forms of ion-exchangeable media can be prepared by traditional means in batch mode. Batch mode means a batch process, as opposed to a continuous process, and is inherently a multi-step processes. Two types of batch mode operations that may be employed are fixed-bed and stirred tank. In the fixed bed approach, one or more static vessels are packed with media and a solution is passed through the media until the media is equilibrated with the solution. In the stirred tank approach, a mixture of media and solution are contacted in a vessel equipped with a mechanism for stirring to establish mixing between the media and the solution. In the stirred tank method, solution and media are mixed until equilibrium is attained. The traditional batch methods suffer from several limitations including inefficiencies, which require a large stoichiometric excess of solution to reach equilibrium throughout the length of the bed. In these batch processes, the waste could be as much as 60% of the total solution used in the process. Thus, more chemicals are consumed and more waste is generated, leading to significant added expense. The added expense of these inefficiencies can significantly impact the feasibility of a commercial process, particularly where these chemicals are expensive, such as the case when precious metals are employed. Another limitation is that the batch methods are inherently multi-stage processes where equilibration and rinse stages must be conducted sequentially, leading to further inefficiency and longer operation time. Another limitation is that large vessels are required. The stirred tank has the additional limitation that repeated batches are likely required to reach the desired media composition at equilibrium. The stirred tank method also suffers from media attrition, due to repeated contact between the stirring mechanism-and the media and long equilibration time.
In a large scale commercial process, in which expensive raw materials, such as precious metals, are being used to prepare the media, the efficiency of the preparation process is very important to the overall process economics. As a means of alleviating the limitations of the traditional methods, the current invention provides a process of increasing production yield by more efficiently utilizing the incoming solution so that the total quantity of chemicals required to reach equilibrium is decreased and effluent waste is decreased. Accordingly, it is an object of an embodiment of the invention to provide an efficient process for preparation of ion-exchangeable media where particular ionic compositions (loadings) are prepared. In an embodiment it is an object to provide a process for modification of the ionic composition of an ion-exchangeable media in an efficient manner within a continuous contacting device. Another object of an embodiment is to prepare media in-situ, within the final processing equipment itself, such that separate preparation, transportation, and filling are not needed. Another object of an embodiment is to prepare media using the continuous contacting device that is homogeneous from column-to-column, within each column, and that is reproducible from one preparation to the next. A still further object in an example of the invention is to provide a process that is readily adaptable to commercial operation.